[loveboom3012]

void update_ds1307(void)
{
	int8 data=0; //luu tru du lieu tam thoi de gui vao ds1307
	i2c_start();
	i2c_write(0xd0);
	i2c_start(0x00);// ghi du lieu bat dau tu vi tri 00
	data=sec1+(sec2<<4);
	data=data&0b01111111;
	i2c_write(data);

	data=min1+(min2<<4);
	i2c_write(data);

	hour=hour1+(hour2<<4);
	i2c_write(data);
	
	data=day;
	i2c_write(data);
	
	data=date1+(date2<<4);
	i2c_write(data);

	data=month1+(month2<<4);
	i2c_write(data);

	data=year1+(year2<<4);
	i2c_write(data);
	
	data=0x00;
	i2c_write(data);
	
	i2c_stop();	
}

phần data=sec1+(sec2<<4);
data=data&0b01111111;
i2c_write(data);
có nghĩa là sao?